4 2 1 Special Features Of Ultrasound example essay topic

CONTENTS 1. Introduction... 3 1.1 History... 3 1.2 Wave structure... 3 2. Ultrasound...

4 2.1 Special features of Ultrasound... 6 3. Sources of ultrasound... 6 3.1 Mechanical emitters... 7 3.2 Electro-acoustic transducers...

8 4. Usage of ultrasound... 10 4.1 Ultrasonic cleaning... 10 4.2 Ultrasonic welding... 10 4.3 Ultrasonic soldering and tin coating... 12 4.4 Production processes acceleration with the help of ultrasound...

12 4.5 Ultrasonic flaw detection... 12 4.6 Ultrasound usage in radio electronics^i^a... 12 4.7 Ultrasound in medical treatment... 13 5. Conclusion... 13 1.

Introduction As long as ultrasound does not appear to be audible due to its high frequency bands the use of it in sound industry (music or film) is insignificant, though it is used for a huge amount of applications in science, industrial production and medical treatment. In this work I will analyze most common ways of ultrasound generation and investigate some ways of its usage. But let us first look how the history of ultra sound started. 1.1 History The research of high frequency oscillations began in 1876, when a British physician Francis Galton generated high frequency sound waves with the help of a device which later was called "Galton Whistle". Along with the flow of gas through a thin pipe high frequency oscillations emerged. Pic.

1 Galton's Whistle But the most significant discovery for the contemporary ultrasonic devices was generating oscillations in crystals with the help of electricity. In 1880 in Paris Pierre and Jacques Curie discovered piezoelectric effect- a production of electricity when applying mechanical pressure to certain crystals (Quartz or Rochelle salt); alternatively, electrostatic stress produces a change in the linear dimensions of the crystal. Piezoelectric crystals - is the fundamental of any contemporary ultrasonic device. 1.2 Wave structure The physical phenomenon of sound waves is an example of oscillating process, and any kind of oscillation presumes deviation from balanced state and described with its characteristic digression from balanced values. Sound represents mechanical vibrations of an elastic environment (solid, liquid or gaseous), which lead to creation of consistently alternating fields of compression and rarefaction so the same refers to ultrasound, though ultra sound has special features which are different from sound waves of audible range. It is easier focused due to its smaller wavelength and as a result you get an increase of intensity of ultrasonic oscillations.

It was discovered that its propagation in gases, liquids and solid objects leads to different phenomena, the majority of which are used in practice in different fields of science and industry. During recent years successful experiments were carried out in the fields of ultrasonic cavitation and acoustic flows, which allowed developing technological processes using ultrasound propagation in liquids. Pic. 2 Acoustic flow generated in carbon oil when exposed to a 5 MHz wave In present time a new branch of chemistry is being developed- ultrasonic chemistry, as well as molecular acoustics. Ultrasound is being started to be used in new fields such as flaw detection testing, holography, quantum acoustics and more. Along with theoretical studies in ultrasonic field a lot of practical experiments were carried out, universal and specialized ultrasonic devices were produced for industrial production were produced, which helped to increase working efficiency.

2. Ultrasound Ultrasound - represents sound waves which appear in the frequency range from 20 KHz to 1000 MHz. Depending on the wavelength and frequency ultrasound obtains different features of emission, reception, propagation and usage, therefore the ultrasonic range is divided by 3 bands: o Low ultrasonic frequencies (2 104-105 Hz); o Middle ultrasonic frequencies (105-107 Hz); o High ultrasonic frequencies (107-109 ~A"o). Elastic waves of the range from 109 to 1013 Hz are called hypersonic sound. The structure of ultrasonic waves (non-audible) does not differ from the waves of audible range.

In liquid and gaseous environments where the density variations are not significant, acoustic waves have longitudinal form which means that the particle oscillations are parallel to the wave propagation. In the solid objects and dense human tissue due to their inconsistent density there appear elastic shift deformations along with longitudinal waves what leads to transverse wave components formation (particle oscillations are perpendicular to the wave propagation direction). The ultrasound propagation obeys basic laws which are the same for acoustic waves of all frequency ranges. These are laws of reflection, refraction, diffraction.

And of course there is a significant matter regarding the ratio between the wavelength and geometrical dimensions D of an obstacle on the way of the wave. In case when D the propagation of sound takes place according to the basic laws of geometrical acoustics which means the wave reflects and refracts, in case when D.